1. Field of the Invention
The present invention relates to a plasma display panel (PDP) that can perform color display.
A PDP is becoming widely available as a wide screen display for a television set after the color display thereof has been succeeded in commercialization. One of the challenges to improve the image quality of the PDP is to enhance reproducible color range.
2. Description of the Prior Art
As a color display device, an AC type PDP having three-electrode surface discharging structure is commercialized. This type has a pair of main electrodes for sustaining, which are arranged in parallel for each line (row) of the matrix display and also has an address electrode for each column. Division walls for preventing interruption of discharge between cells are provided in stripes. A surface discharging structure includes a substrate on which the pairs of main electrodes are arranged and an opposing substrate on which a fluorescent layer for color display is arranged, so that deterioration of a fluorescent layer due to an ion impact upon discharge can be reduced to obtain a longer life. The “reflection type” that has the fluorescent layer on the back substrate is superior to the “transparent type” that has the fluorescent layer on the front substrate concerning light emission efficiency. In general, Penning gas containing neon (Ne) and a trace of xenon (Xe) (4-5%) is used as a discharging gas. When the discharge between main electrodes occurs, the discharging gas radiates ultraviolet rays, which excite the fluorescent material to emit light. Each pixel includes three cells for red (R), green (G) and blue (B) light colors, and the ratio of the three light colors decide the display color. The amount of light emission of each cell depends on the number of discharge times per unit time.
The conventional PDP has a problem in that the color temperature of white is low compared with other displays (especially with a CRT). The reason is that the light intensity of the blue fluorescent material is lower than the light intensities of the red and the green fluorescent materials, and that the neon as the discharging gas emits orange light.
It is necessary to optimize the relative light intensities (balance of luminous intensities) of the R, G and B cells for obtaining a desired color tone when trying to display white color by applying the same number (the maximum number within variable range) of voltage pulses to the R, G and B cells.
There is a method for adjusting the luminous intensity, in which a conversion efficiency of the fluorescent material, the thickness or the shape of the fluorescent layer is selected. However, this method has the following problems.
1) It is not easy to adjust the conversion efficiency of the fluorescent material.
2) The thickness or the shape of the fluorescent layer can be adjusted only within the range that does not affect the discharge.
3) The control of the thickness and the shape of the fluorescent layer has low repeatability.
In addition, in order to set the number of voltage pulses to apply, that is, the number of discharges for each color so as to display white color having a desired tone, the number of voltage pulses for the color with the minimum intensity should be maximized and the number of voltage pulses for other colors should be smaller than that. Therefore, the variable range of the light emission amount is narrowed, resulting in deterioration of the gradation reproducibility.
Furthermore, there is another method in which the area of the fluorescent layer is selected for each color. In this method, stable driving is difficult since the size of the cell depends on the color, and the margin of the driving voltage is narrowed. Namely, if the size of pixel is fixed when the cells have different sizes, the cell size of at least one color becomes small compared with the cell size that is the same for three colors. Since the firing potential rises when the cell size is reduced, the voltage margin is narrowed.